Die Entwicklung prospektiver Diapause-Keime (Bombyx mori L.) in vitro ohne Dormanz: II. Fremdeiwei�medium (LYS) mit extraembryonalem Depotmaterial aus verschiedenen Phasen der Eidiapause

Sorbitol as an arrester of embryonic development in diapausing eggs of the silkworm, Bombyx mori

Recently, it was confirmed that embryos derived from diapausing eggs of the silkworm, Bombyx mori, begin their development and reach larval maturity on mulberry leaves, when the naked eggs are cultured in vitro. In this study, we found that the method of embryo culture is useful for determining the physiological regulation of diapause. We show that the development of embryos derived from diapausing eggs was strongly inhibited by the addition of either sorbitol or trehalose to the culture medium. Furthermore, this inhibitory effect disappeared when the embryos were cultured in a control medium which did not contain either sorbitol or trehalose, indicating that the inhibitory reactions caused by both substances are reversible. The minimal effective dose of either sorbitol or trehalose was approximately 0.2 M, a value similar to the in vivo concentration of sorbitol in diapausing eggs (0.2 M). Glycerol, mannitol or glucose were moderately effective for inhibition. Sorbitol present in diapausing silkworm eggs does not appear to serve as an antifreeze, but as an strong arresting factor of embryonic development. Furthermore, these results show that a decrease in sorbitol releases the embryos from diapause at the termination of diapause.

Oxygen consumption in relation to sorbitol utilization at the termination of diapause in eggs of the silkworm, Bombyx mori

Rates of oxygen consumption were followed throughout the entire period of diapause in eggs of Bombyx mori. In non-diapause eggs at 25 degrees C, O(2) uptake was divisible into three phases, corresponding to morphogenetic processes. In diapause eggs at 25 degrees C, O(2) uptake showed a peak (100 &mgr;l/g eggs/h) at 1 day and then suddenly dropped to reach a level of 8-10 &mgr;l/g eggs/h at 10 days and thereafter. To break diapause, eggs were exposed to 5 degrees C for varying periods. When O(2) uptake was measured at 5 degrees C, it remained at 6 &mgr;l/g eggs/h. When eggs were chilled for increasing periods and O(2) uptake was measured immediately after warming to 25 degrees C, the rates increased after a lag phase. In HCl-treated eggs, O(2) uptake increased immediately after acid-treatment. In all cases, highly increasing O(2) uptake at 25 degrees C coincided with termination of diapause. These results were discussed in relation to sorbitol utilization at the termination of diapause.

The embryonic diapause of Aulocara elliotti (Orthoptera, Acrididiae). Histological and morphometric changes during diapause development and following experimental termination with juvenile hormone analogue

Progressive hypertrophy of fat body, muscles, gonads and pleuropodial glands was observed with lengthening diapause incubation in embryos of Aulocara elliotti. Embryonic hemolymph stained more darkly and lipoid materials accumulated in the fat body and other tissues. Gradual increase in volumes was observed in the corpora cardiaca, corpora allata and ventral head glands (ecdysial glands). Termination of diapause was achieved in embryos treated with juvenile hormone analogue (JHA) (4 ethyl phenyl 6.7 epoxy geranyl ether--87%, Stauffer Chemical) applied directly to the egg undiluted or when eggs were immersed in a 10% solution in methanol. Treated embryos terminating diapause underwent rapid teratological morphogenesis, achieving pigmentation and sclerotization as in definitive embryos without engulfing their yolk. In treated embryos which remained in diapause, unusual paired masses of pigmented cells, resembling the melanotic pseudotumors of Drosophila, were observed ventral and lateral to the stomodeum and are thought to be subesophageal body cells (pericardial cell homologues). In some embryos these cells were enlarged, lysed or their nuclei rhexic and pycnotic. This response suggests these cells are target organs for JHA, or perhaps for ecdysone or its precursor released by JHA treatment. Endocrine glands in treated embryos had significantly larger volumes (.01) than those of controls or untreated embryos. The ventral head glands of treated embryos appeared to be cytoplasmically depleted. It is suggested that JHA triggered the release of stored ecdysone (or its precursor produced in the ventral head gland) at a rate too rapid for normal morphogenetic processes, such as dorsal closure, to accompany epidermal maturation. The response to JHA cannot be interpreted as juvenilization, but rather must be considered to be precocious maturation. These results indicate that: 1. diapause development involves a transfer of nutrient materials from the yolk into the fat body and other embryonic tissues where they are available to meet the demands of post-diapause morphogenesis; 2. that embryonic diapause in A. elliotti is a consequence of endocrine deficiency which probably results ultimately from the lack of neurosecretory stimulus from the brain-corpora cardiaca complex; and 3. that the subesophageal body cells, and perhaps the pericardial cells, play an essential role in the embryonic physiology, perhaps in the production of carrier protein and/or an essential growth regulator.

[Development of prospective diapause-germs (Bombyx mori L.)in vitro without dormancy : III. Their competence and interference inLYS-media, without extraembryonic storage material]

In a foreign protein medium (LTS), naked prospective diapause-germs have a tendency to develop into fully segmented germ bands (stage of dormancy): however, deposition of chorion, serosa or yolk will stimulate themvia the medium to pass through organogenesis without delay (non-dormancy =Nd). The question remained if a germ from a non-diapausing egg would stimulate the uninterrupted development of such a test-germ (Tk). Using 2 different or 2 to 3 equal germs as well asTk alone (control) in hanging drops, experimental evidence was obtained permitting conclusions not only as to the competence and sensitivity of the embryonic reaction system, but also as to factors of the extraembryonicNd-action systems in eggs with and without predetermined diapause regulatory mechanism. 1. Control explants (1 prospective diapause-Tk inLYS) have aNd-level of 10% (= average ofNd-rates in operative stages). This difference from former controls (0%Nd) can be explained by the longer operative procedure in the cups when several test-germs were used. Seven minutes after opening an egg one can reckon on aNd-stimulationvia LYS medium from egg-residues in the operation cup. While transfering the test-germs, yolk-derived substances related to theNd-stimulation can be brought into the hanging drop. The difference betweenNd-controls and the results ofNd-stimulation have to be statistically significant. 2. In experiments with two different germs in LYS-droplets no influence of a non-diapause germ (polyvoltine) on a prospective diapause germ (univoltine) could be noted. Accordingly, the naturally prospectiveNd-germs, have a tendency to develop to dormant germs only, as do the 2Tk and 1Tk controls. In combination with artificially prospectiveNd-germs (univoltine, HCl-treated) no stimulation of the test germ occcurs; nor after explantation with an older germ-band or a young embryo. 3. Combination with two prospective diapause germs of equal age in a drop, having the same minor contamination ofNd-factors in the operation-cup, will result in a threefold increase of theNd-level as compared to the 1Tk-controls. The competence of the embryonic reaction system ranges from a coatlike germ-anlage to a germ with thoracic segmentation. In the dish-like germ-anlage at diapause onsetin ovo maximalNd-rate (70%) is foundin vitro, i.e. highest sensibility towardsNd-stimulatory factors. Also at this operative stage, bothTk of a drop, most frequently developed beyond the dormancy stage. 4. Experiments with three prospective diapause germs of equal age in a drop, having the same minor contamination ofNd-factors in the operation-cup, show a sevenfold increase of theNd-level as compared to controls, showing an almost similar stage-range in competence and stage-specificity in sensibility. The increase of theNd-stimulation rate in relation with the number of test germs in the drop corresponds to a morphogenetic crowding-effect, the influence of the test germs on each other being called "interference". 5. Experiments with LYS-media which was slightly contaminated with bacteria and then refiltered had a 42%Nd-level in the 1Tk experiments. This significant difference from the 10% control level can be related to a sensitivity increasing factor or to aNd-stimulating "masterkey"-effect of the bacterial products in addition to the yolk factors already present. The 65%Nd-level in the 2Tk experiments clearly indicates "interference". 6. Interference was also shown inexperiments with artificially prospective non-diapause germ of the same age. Test-germs isolated immediately after the HCl-treatment had a very highNd-rate (78% in 2Tk and 100% in 3Tk). Interference also occurred in germ-bands that were removed at a later stage, i.e.in ovo prior to organogenesis (2Tk, 60%Nd-rate instead of 1Tk, 20%Nd-rate). Consequently, interference may be caused by a factor promoting an overall increase of tissue activity. 7. Critical evaluation of the methods and discussion of the resultsin vitro permit the following conclusions as to the developmentin ovo. Up to organogenesis, the continuous development of the germ-anlage (non-dormancy), is stimulated by an extra-embryonic system. In particular, the yolk-cell system contains factors, without which all germ-bands (including nondiapausal eggs fromBombyx and presumably other insect eggs) can only pass autonomously through the already programmed and/or determined gastrulation and segmentation. In pre-determined egg-diapause, an extra-embryonic dormancy regulatory mechanism inactivates thisNd-action system. Maternal hormonal depots may influence the continuous stimulation of cell division and the information-transfer for the programming of organogenesis. The activation of enzyme-systems inNd-stimulation can be imitatedin vitro by bacterial contamination and by interference from test germs of the same age, and may be appear as increased sensibility of the test germs.